It is known through U.S. Patent Application Publication No. 2002/0143331, FIG. 9, of an interspinous vertebral implant including first and second supports defining fixation bodies to respective adjacent spinal processes and in between which is placed, an elastic body of annular shape and coaxial with the supports. The elastic body is placed between the bottom of an annular cavity of the first support and an annular male body of the second support which is axially guided in this cavity. The peripheral wall of the first support includes an internal annular protuberance which can cooperate with an annular shoulder of the male body of the second support in order to limit the gaps of the supports. The face of the extremity of the peripheral wall of the first support constitutes also a stop which can cooperate with an edge of the second support in order to limit the compression of the elastic body.
According to U.S. Patent Application Publication No. 2002/0143331, this implant presents several disadvantages. At first instance, it can be noted that this implant and its elastic body have a circular shape. To obtain a certain capacity of shock absorption, the elastic body must have sufficient dimensions. Yet if the diameter of the implant is increased, its overloading in the antero-posterior direction will be too great and will necessitate the damaging, in too great of a measure, of the vertebral tissues for the setting in place of the implant. On another hand, the presence of the annular male body of the second support and of the peripheral wall of the first support limit in great fashion, the space available for the elastic body. Another disadvantage is that the stops which limit the gaps of the supports appear undersized in order to really resist to physiological loads.
FR Patent Application No. 2 774 581, diagram 4, describes an interspinous vertebral implant consisting of first and second supports defining in their center part respective fixation bodies for spinal processes of two respective vertebrae, these fixation bodies being located in the same sagittal plane, and first and second elastically compressible bodies in the direction of the spine, these elastically compressible bodies being put in place between the first and second supports and on both sides of the aforementioned sagittal plane.
The elastically compressible bodies are in the shape of bellows defining waterproof inner walls filled with a liquid and a core made in a viscoelastic material. This implant according to FR 2 774 581 seems to present a greater capacity of shock absorption than the one described in the document U.S. Patent Application Publication No. 2002/0143331. However, this implant appears to be difficult to achieve because its extremities of the bellows must be solidly fastened to the supports in order to maintain the inner walls waterproofed and to avoid the separation of the supports from one another. Yet, FR 2 774 581 does not explain how to fasten the bellows to the supports. This problem of bellows' fixation to the supports is that much more critical, given that the implant does neither comprise any stops to limit the supports gap nor to limit the bellows' compression. It is important to also note that the viscoelastic cores are not really guided and therefore susceptible to move laterally, which can unbalance the implant and perturb the functioning of the bellows.